Make sure sysupgrade on NAND also works in case of UBI volumes having
index >9. While at it, also make sure UBI device is detected and abort
in case it isn't. Use Shell built-in shorthand ':' instead of 'true'.
Fixes#9708
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 0dbca1b2baf9c26514b517a1e5860f6a5b04d5ae)
6fe3852d47